The present invention relates to an improved ring carrier used for improving wear resistance in the piston ring grooves of pistons for internal combustion engines, particularly pistons made from cast aluminum alloys. The present invention also relates to a method casting-in the ring carrier integrally in an aluminum alloy piston.
In this specification, the term "ring carrier" is used to refer to all of the ring carriers by itself before it is integrally cast-in the piston, the ring carrier that has been integrally cast-in the piston, and the ring carrier that has been finished via machine processing.
Ring carriers, generally made from stainless steel or cast Niresist, are used for aluminum alloy pistons in order to improve wear resistance at the attachment groove of the piston ring.
When casting this type of piston, the ring carrier is set inside the mold, and the ring carrier is integrally cast-in by filling the mold with a molten aluminum alloy. Conventionally, an annular ring flange of a square section is formed on the outer periphery of the ring carrier so that the ring can be mounted and fixed in the mold.
In general, the following processes are involved in casting in a ring carrier. The ring carrier is immersed in molten aluminum beforehand to produce an adequate bond layer between the ring carrier and aluminum. The bond layer with aluminum is produced over the entire surface of the ring carrier. Then the ring carrier is fixed in the mold in such away that excess space is formed between the ring carrier fixed in the mold and the outer mold so that the entire ring carrier can be totally surrounded by the molten metal poured in the mold. Thus the ring carrier is cast-in and metallurgically bonded with aluminum alloy piston.
When using a ring carrier with a flange as described above, the maximum outer diameter of the ring carrier used is greater than that of the piston. This requires the piston cast to have a larger outer diameter. This is wasteful of raw materials and uneconomical. Furthermore, the precision in the attachment of the ring carrier to the mold is lowered and automation of the attachment process is made difficult. Considerable excess mass gets left on the piston cast around the flange. This makes extra steps in the machine-processing stage necessary to eliminate the excess mass and also results in a great deal of chips comprising mixtures of aluminum and Niresist cast iron or stainless steel.